Electron-Iron Recombination Rate Coefficients and Photoionization Cross Section for S XIV and SXV for X-ray and UV modeling

ABSTRACT

The processes of photoionization and electron-ion recombination of (hν+SXIV ⇌ SXV+e)and (hν+SXV ⇌ SXVI+e) are studied in detail using ab initio unified method that provides self-consistent sets of results for these processes. Result are presented for large number of fine structure levels when n≤ 10 and 0 ≤ l ≤ 9; 98 levels for Li-like S XIV with 1/2 ≤ J ≤ 17/2 and 188 levels for He-like S XV with 0 ≤ J ≤ 10. Photoionization cross section, σPI, of the levels of both S XIV and S XV decay smoothly in the lower region. However, narrow and high peak autoionization Rydberg series of resonances belonging to to various excited core levels appear in the high energy region and enhance the background cross section of the excited levels. The resonance series of n=2 core levels dominated while they become weaked in higher n. The prominent feature is the enhancement of the background cross section at n=2 core thresholds due to K-shell ionization leaving the ion in excited 2p states. σPI also show wide PEC (photo-exciting-of-core) resonances at the photon energies that equal to the core exciting energies. Level-specific photoionization cross sections, σRC (nSLJ), and recombination rate coefficients , αRC(nSLJ), are obtained for the first time for these ions. Currently available results correspond to photoionization for LS terms with missing features and to only total recombination rate coefficients. Present σRC (nSLJ) incorporates both the radiative recombination (RR) and dielectronic recombination (DR), and show a 'bump' or 'shoulder' in the high temperature region due to DR dominance. The total unified recombination rate coefficients show good agreement with the available DR and RR rates. Recombination rates over photoelectron energy are presented by astrophysical and laboratory plasma applications. Total recombination rates for H-like S XVI are given for completeness. The results should be accurate within 10-15% based on the unified method that includes important atomic effects such as radiation dumping, channel couplings, interference of DR and RR, and relativistic fine structure effects. The comprehensive datasets are aplicable for various models such as for ionization balance and recombination -cascade for UV and X-ray lines.

PACS numbers: 32.30.-r;32.30.Jc, 32.30.Rj; 32.80.Fb